Direct bonding means a bonding technique for manufacturing a display device in which a plurality of optical members, for example, a touch panel and a display panel, and the like are combined into one. The direct bonding can be referred to as a term such as optical bonding, full lamination or screen fit.
The properties required for bonding agents used in direct bonding include heat resistance, cohesive force, adhesive force, transparency and the like, and recently, in particular, the demand for high heat resistance performance is increasing.
It is necessary to develop a bonding agent having high heat resistance performance and adhesive force simultaneously, where a bonding agent having excellent performance can be prepared by using advantages of acrylics having low cost and excellent adhesive force and silicone materials having excellent heat resistance. Patent Document 1 (JP Laid-open Patent Publication No. 2014-001341) discloses a curable resin composition using the silicone and the acrylic.
However, the preceding document lacks mention of physical properties related to the direct bonding process. A typical process of the direct bonding is Dam & Fill process. The Dam & Fill process is a laminating process by pre-curing a dam using a photo-curable resin composition, and then coating an active region with the photo-curable resin composition to completely cure it.
However, the Dam & Fill process has a problem that a lot of defects are generated in the laminating process. For example, if the elastic modulus upon pre-curing is too high, it is difficult to maintain a gap due to restoring force after lamination, so that air bubbles may occur between the dam and the fill. On the other hand, if the elastic modulus is too low, there is a risk that the photo-curable composition of the fill region bursts out upon laminating.